The present invention is related to a polyaryletherketone (PAEK)-powder, which is particularly suited for the use in a rapid prototyping method, to a method for producing such a powder as well as to a rapid prototyping method for the manufacturing of a three-dimensional object, in which method this powder is used.
Methods, in which a quick manufacturing of prototype parts starting from construction data is possible, are referred to as rapid prototyping methods. Usually the part to be manufactured is built layer-wise from a shapeless material or a material that is neutral with respect to shape. For the case that the original material is in powder form, such methods are for example known under the names 3D-laser sintering, 3D-laser melting or 3D-printing. Here, metals, ceramics and last but not least plastics are used as basic materials. For instance, U.S. Pat. No. 5,730,925 describes a laser sintering method, in which layers of a powder are applied onto a support that can be vertically moved and in which the layers are selectively sintered at the positions corresponding to the cross-section of the object to be manufactured by means of a laser.
FIG. 3 shows as an example a laser sintering device by means of which a method for a layer-wise manufacturing of a three-dimensional object may be performed. As is apparent from FIG. 3, the device comprises a container 1. This container is open to the top and is limited at the bottom by a support 4 for supporting an object 3 to be formed. By the upper edge 2 of the container (or by its sidewalls) a work plane 6 is defined. The object is located on the top side of the support 4 and is formed from a plurality of layers of a building material in powder form that can be solidified by means of electromagnetic radiation, which layers are in parallel to the top side of the support 4. The support may be moved in a vertical direction, i.e. in parallel to the sidewall of the container 1, via a height adjustment device. Thereby the position of the support 4 relative to the work plane 6 can be adjusted.
Above the container 1 or rather the work plane 6 an application device 10 is provided for applying the powder material 11 to be solidified onto the support surface 5 or a previously solidified layer. Also, an irradiation device in the form of a laser 7, which emits a directed light beam 8, is arranged above the work plane 6. This light beam 8 is directed as deflected beam 8′ towards the work plane 6 by a deflection device 9 such as a rotating mirror.
When the three-dimensional object 3 is manufactured, the powder material 11 is applied layer-wise onto the support 4 or a previously solidified layer and is solidified at the positions of each powder layer that correspond to the object by means of the laser beam 8′. After each selective solidification of a layer the support is lowered by the thickness of the powder layer to be subsequently applied.
The properties of the original powder material are selected depending on the desired properties of the part to be manufactured. However, as a rule a high bulk density as well as a sufficient pourability are of great significance. In order to guarantee a high accuracy of the details and a high surface quality of the objects to be manufactured, plastic powders are necessary that have an upper particle size limit of less than 150 μm and a fraction of 90% below 135 μm (D0.9-value). Furthermore, the powder should not exceed a D0.1-value of 32 μm in order to ensure a stable layer application. Also, a spherical grain shape of the powder particles is indispensable for ensuring a uniform and smooth powder bed surface and part surface. In addition, a small surface roughness of the particles, expressed as BET surface, has to be aimed at, because thereby the powder bed density is increased and built-up processes and degradation processes, which negatively affect the processability of the powder, are reduced.
Among plastic powders mainly polyaryletherketones are of interest. The reason is that parts that have been manufactured from PAEK powder or PAEK granulates are characterized by a low flammability, a good biocompatibility as well as a high resistance against hydrolysis and radiation. It is the thermal resistance also at elevated temperatures as well as the chemical resistance that distinguishes PAEK powders from ordinary plastic powders. Due to these properties there is a high demand for PAEK materials particularly in the aerospace industry, in the automotive industry and in the electronic industry as well as the medical industry. In particular, such a PAEK polymer powder may be a powder from the group consisting of polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyetherketone (PEK), polyetheretherketoneketone (PEEKK) or polyetherketoneetherketoneketone (PEKEKK).
Therefore, the great potential of the material PAEK in relation to a generative rapid prototyping method such as laser sintering is apparent. However, tests of the inventors using PAEK powders as they are used in conventional methods for manufacturing of parts showed that these powders are suitable for laser sintering only to a limited extent, because the above-mentioned requirements on the powder properties are not fulfilled:
In particular above already exposed areas it became obvious that the layer application leaves a lot to be desired with respect to uniformity and that the unevenness of an applied layer affected the accuracy of the manufacturing of the parts. An insufficient pourability as well as a bulk density of the powder that was too low were identified as reasons for this.
Furthermore, it was found that the powder bed density in the applied powder layer was very low. This was regarded as indication to the fact that the bulk density of the particles of the commercially available powder was not high enough. However, a small powder bed density prevents the formation of parts having a high density and strength.